In the present-day telecommunication environments, so-called point-to-multipoint services, which allow data to be transmitted from a single source point to multiple endpoints, are commonly known. In addition to the fixed networks, these services are expected to be used extensively in mobile and wireless networks.
This has been attended to in the standardization work of the 3rd Generation Partnership Project (3GPP) by defining a service called the Multimedia Broadcast/Multicast Service (MBMS), which is a unidirectional point-to-multipoint bearer service in which data is transmitted from a single source entity to multiple recipients. The MBMS has two modes of operation: a broadcast mode and a multicast mode. When using MBMS, data is transmitted over a common radio channel in order to efficiently use radio/network resources. In the broadcast mode the data is transmitted to all users in one or more broadcast areas, whereas in the multicast mode the data is transmitted to a multicast group in a multicast area. The multicast group is a group of users who have activated the service in the multicast mode and are therefore capable of receiving the data.
In the on-going standardization process of studying the architecture of the Multimedia Broadcast/Multicast Service, one of the main problems is how to initiate the service efficiently, without wasting network resources. In the 3GPP specification TS 23.846, for example, it is required that “in the multicast mode, MBMS should support multicast resource allocation whereby data transmission to a multicast group is carried out in a certain cell only if multicast group members are to be found in that cell”. However, a problem related to this is that the current cell of a mobile station that has joined a multicast group is not always known, i.e. if the mobile station is in a state where its current cell is unknown to the network.
The standardization process has brought about several proposals for initiating multicast data transfer and establishing a radio access bearer for the service. Some of the proposals suggest the use of traditional paging to find out the current cells of the mobile stations which have joined the multicast group. However, traditional paging mechanisms are not preferred in finding out the whereabouts of the mobile stations, since paging may cause a plurality of mobile stations to reply simultaneously or within a short period, which in turn may cause congestion on the uplink signaling channel.
Version 1.1.1 of the above-mentioned specification TS 23.846 suggests that in a multicast case, the SGSN (Serving GPRS Support Node) sets up the radio resources on a Routing Area basis, i.e. for the Routing Areas where members of the multicast group have been detected. Thus in this case the mobile stations are not required to perform any uplink signaling in order to indicate their presence and/or willingness to receive the service, but the radio resources are set up immediately in the above-described manner. However, a major drawback of this method is that it wastes network resources, since the resources are set up for all RNCs (Radio Network Controllers) serving the Routing Area, even though there would be no MBMS capable users under the RNC's coverage area.
It is an objective of the invention to bring about a solution whereby it is possible to avoid the above-mentioned drawbacks.